Examples of methods for producing a toner by rendering a dispersion liquid or solution of a toner composition into droplets and drying and solidifying the droplets include a spray drying method with an atomizer (refer to PTL 1).
However, since particles obtained by a conventional spray drying method have relatively large particle diameters and a wide particle size distribution, it is difficult to form a toner with a sharp particle size distribution.
Regarding a method for producing a toner intended to take the place of the foregoing, there have been proposed a method and an apparatus in which fine droplets are formed utilizing a piezoelectric pulse, and the fine droplets are dried and solidified so as to form a toner (refer to PTL 2). Further, a method and an apparatus have been proposed in which fine droplets are formed utilizing thermal expansion that takes place inside a nozzle, and the fine droplets are dried and solidified so as to form a toner (refer to PTL 3).
However, the methods and the apparatuses described in PTLs 2 and 3 merely allow ejection of droplets from one nozzle using one piezoelectric material, and thus the number of droplets able to be ejected per unit time is small, thereby leading to poor productivity. Moreover, the employed structure in which a dry gas flow is supplied for each ejecting portion is inevitably complex and thus uneconomical.
Accordingly, as a toner producing method and apparatus capable of a plurality of ejections of droplets using one vibration source, there have been proposed a method and an apparatus in which a nozzle is vibrated by the expansion and contraction of a piezoelectric material serving as a vibration generating unit, droplets of a toner composition fluid are thereby ejected from the nozzle at a constant frequency, and the droplets are dried and solidified so as to form a toner (refer to PTL 4). Also, a method and an apparatus have been proposed in which there are provided an ejecting member having ejection holes, and a vibration generating unit configured to provide vibration to the ejecting member at a predetermined frequency, the ejecting member is vibrated so as to serve as a vibrating member, droplets are thereby ejected from the ejection holes, and the droplets are dried and solidified so as to form a toner (see PTL 5).
Since the toner producing methods and apparatuses described in PTLs 4 and 5 enable a plurality of ejections of droplets using one vibration source, it is possible to efficiently produce a toner with a relatively sharp particle size distribution. However, if the ejection direction of the droplets and the direction of a dry gas flow are not controlled, the gas flow will advance in an unintended direction, and thus unification (amalgamation) of initial droplets may be inevitable, especially in a frequency range over 100 kHz.
Accordingly, as a method for producing a toner capable of preventing unification (amalgamation) of droplets, there has been proposed a method wherein there is provided a gas flow forming unit configured to form a gas flow which passes through a narrowed portion (that corresponds to a nozzle formation area and that is placed on a downstream side with respect to a droplet discharge direction) and which advances in the droplet discharge direction, whereby the space between droplets is widened, the droplets are dried, solidified and rendered into a toner, preventing unification of the droplets, and a toner with a sharper particle size distribution is thus produced (refer to PTL 6).
However, the method for producing a toner described in PTL 6 does not suffice to prevent unification (amalgamation) of initial droplets and thus leaves room for consideration.